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  • 1

    Multispectral Imaging and Microscopy

    13 November 2016 Giovanni Verri

    Summary (Imaging): •  Introduction: Light/Radiation sources, filters and recording devices

    •  Multispectral imaging techniques:

    •  Visible-reflected/transmitted •  Infrared-reflected/transmitted •  Ultraviolet-reflected •  Ultraviolet-induced luminescence •  Visible-induced luminescence •  False-colour images

    Summary (Microscopy): •  Microscopy:

    •  USB microscopy •  PLM (cross sections, thin sections and dispersions) •  Fluorescence and Confocal microscopy •  SEM-EDX

  • 2

    A sequence of investigations: •  Physical and conservation history → inform targeted observations and

    investigations;

    •  Visual examinations → inform targeted observations and investigations;

    •  imaging → provides additional information on the x and y axes and some on the z axis: SPATIAL INFORMATION;

    •  Additional non-invasive point analysis (FTIR, XRF, luminescence spectroscopy, etc.);

    •  Identification of the sampling area;

    •  Cross sections and other invasive investigations.

    This process is iterative! Questions raised by observations or investigations inform further targeted investigations.

    IT ER

    AT IV

    E

    Visible

    A variety of techniques, a variety of information

    Infrared- reflected

    Ultraviolet- reflected

    Ultraviolet- induced luminescence

    Visible-induced luminescence

    Raking light

    Stele of Kleonymos, Hadymos, Peukolaos and Krino. Vergina Museum ΒΛ 3

    Multispectral vs hyperspectral

    3 bands up to 100 bands Many more bands = imaging spectroscopy

    http:// article.sciencepublishinggroup.co m/html/10.11648.j.ajbls.s. 2015030203.16.html

  • 3

    Multispectral vs hyperspectral

    3 bands up to 100 bands Many more bands = imaging spectroscopy

    Multispectral vs hyperspectral (Haida Liang)

    3 bands or more

    •  Allows to identify and distinguish materials – high accuracy

    •  High-tech equipment

    •  Time-consuming

    •  Considerable expertise

    •  Not cheap (…still)

    •  Not really an analytical technique – low accuracy

    •  Low-tech equipment

    •  Fast

    •  Somewhat easy to interpret

    •  Can be very cheap

    Many more bands = imaging spectroscopy

    Multispectral vs hyperspectral

    5 bands (or more) Many more bands = imaging spectroscopy

    UV – B – G – R - IR

  • 4

    Multispectral vs hyperspectral

    5 bands (or more) Many more bands = imaging spectroscopy

    UV – B – G – R - IR

    Visible

    A variety of techniques, a variety of information

    Infrared-reflected

    •  Infrared radiation is penetrative, so may provide information on concealed features (e.g. underdrawings);

    •  When combined with visible imaging, may help discriminating between similar materials or between original and non-original materials.

    False-colour infrared

    Visible

    A variety of techniques, a variety of information

    Ultraviolet-reflected

    •  Ultraviolet radiation is not penetrative, so may provide information on the surface (e.g. coatings);

    •  When combined with visible imaging, may help discriminating between similar materials or between original and non-original materials.

    False-colour ultraviolet

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    Visible

    A variety of techniques, a variety of information

    Ultraviolet-induced luminescence

    •  Characterisation of materials; •  Distribution of materials;

    •  Condition assessment.

    Visible

    A variety of techniques, a variety of information

    Visible-induced luminescence

    •  Characterisation of some specific materials (e.g. Egyptian Blue, Han blue, Han purple, Cadmium pigments, lakes);

    •  Distribution of materials; •  Condition assessment.

    Visible

    A variety of techniques, a variety of information

    •  Distribution of materials; •  Condition assessment;

    •  Identification of a sampling strategy.

  • 6

    Light and Radiation: the electromagnetic spectrum

    Imaging captures distribution maps of the interaction between light/radiation and matter

    UV

    IR

    Three-way system (interaction between radiation and matter):

    Recording device Radiation source

    Object

    Reflection Reflection

    Interaction between light/radiation and matter

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    Reflection Absorbtion Reflection

    UV

    IR

    Interaction between light/radiation and matter

    Absorbtion Absorption

    IR

    Reflection Reflection

    UV

    IR

    Interaction between light/radiation and matter

    Absorbtion Absorption

    IR

    UV

    IR

    Transmission

    Reflection Reflection

    UV

    IR

    Interaction between light/radiation and matter

  • 8

    Reflection Reflection

    UV

    IR

    In te

    ns ity

    nm

    400

    700

    400

    500

    600

    700

    Interaction between light/radiation and matter

    Reflection Reflection

    UV

    IR

    In te

    ns ity

    nm

    % R

    ef le

    ct an

    ce

    nm

    400

    500

    600

    700

    400

    500

    600

    700

    × =

    Interaction between light/radiation and matter

    Reflection Reflection

    UV

    IR

    In te

    ns ity

    nm

    % R

    ef le

    ct an

    ce

    nm

    400

    500

    600

    700

    400

    500

    600

    700

    In te

    ns ity

    400

    500

    600

    700

    × =

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    Reflection Transmission

    UV

    IR

    In te

    ns ity

    nm

    % T

    ra ns

    m itt

    an ce

    nm

    400

    500

    600

    700

    400

    500

    600

    700

    In te

    ns ity

    400

    500

    600

    700

    × =

    % R

    ef le

    ct an

    ce

    nm

    400

    400

    500

    600

    700

    % Tr

    an sm

    itt an

    ce

    nm

    400

    500

    600

    700

    % A

    bs or

    pt io

    n

    nm

    400

    500

    600

    700

    nm

    500

    600

    700

    400

    Reflection

    Absorption

    Tr an

    sm iss

    ion

    + +

    =

    Se ns

    iti vi

    ty

    nm

    400

    500

    600

    700

    800

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    900

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    Sensitivity of the camera sensor

    Sensor pixels

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    Se ns

    iti vi

    ty

    nm

    400

    500

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    Sensitivity of the camera sensor

    Sensor pixels

    Se ns

    iti vi

    ty

    nm

    400

    500

    600

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    800

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    900

    1000

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    Sensitivity of the camera sensor

    Sensor pixels

    Coloured filters

    Se ns

    iti vi

    ty

    nm

    400

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    800

    900

    900

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    Sensitivity of the camera sensor

    Sensor pixels

    Coloured filters

  • 11

    Se ns

    iti vi

    ty

    nm

    400

    500

    600

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    800

    900

    900

    1000

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    Sensitivity of the camera sensor

    Sensor pixels

    Coloured filters

    Se ns

    iti vi

    ty

    nm

    400

    500

    600

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    800

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    900

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    Sensitivity of the camera sensor

    Sensor pixels

    Coloured filters

    Se ns

    iti vi

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    nm

    400

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    800

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    900

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    Sensitivity of the camera sensor

    Sensor pixels

    Coloured filters

    IR-UV- blocking filter

  • 12

    Se ns

    iti vi

    ty

    nm

    400

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    600

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    800

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    900

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    Sensitivity of the camera